text:
How far ahead does an airline know which aircraft you will be flying on?
My favorite features of the United Airlines app are:

you are able to see what specific aircraft will be operating your flight
you are able to trace that aircraft back indefinitely via the "Where is this aircraft coming from?" button

I noticed that each aircraft has a specific number aside from the aircraft model (e.g Boeing 737-900 #3815), that references which specific aircraft will be operating your flight.
My question is how far ahead does an airline plan which specific aircraft will be operating a flight?
I'm not asking if the airline knows that a B737 model will be operating a flight, but I'm asking more specifically how far ahead do they know which specific aircraft in the fleet will be operating a particular flight?
This question may be broad as I realize that it may differ between airlines. I'm just curious as I like to see where my flights have been and will go, I find this very interesting.

It depends on the airline and their planning capacity. The simple answer is that they can't be sure of the tail number "of record" for a flight until the plane pulls into the gate at its destination. It's rare for a plane that departs the gate for a flight to not run that flight (it's pretty bad business for it to be common for flights to depart the gate and then come right back, or to be diverted, or otherwise not finish the route they left the gate to fly); it indicates a mechanical issue exists that did not develop and/or was not discovered until taxi or takeoff, and at some point in the flight (probably when departure control hands them off the the ARTCC) the plane could be said to have "run" the flight even if it ended up diverted.
Most of the equipment schedules (which tail number will fly which route at exactly what departure and arrival times) are generated by computer and can be set up months in advance if they really wanted to. However, that's usually an exercise in futility along the lines of predicting the weather more than a few days ahead. Airline scheduling, like weather, is susceptible to "chaos theory", because small deviations from the initial plan tend to compound over time instead of factoring out.
Ticket sales, rebooks and cancellations will affect the schedule days and weeks in advance of the flight. It's technically illegal to cancel a flight less than a certain number of days before its scheduled departure if it has even a single paying customer on the roster, but if a route is underperforming, the scheduler can reduce the scheduled daily flights along that route which could bump people who bought a ticket far in advance. Also, an underbooked flight can legally be cancelled if the plane is needed for an equipment change on a fuller flight, as cancelling the underbooked flight would cause less overall disruption than cancelling the full flight because that plane can't make its next hop.
I just mentioned mechanicals; that's a big reality check for a computer-generated schedule. If a plane cannot continue because of a mechanical defect, it gets pulled for maintenance. Airlines typically have a few planes parked strategically on the tarmac of various airports for a day, which can be activated to run a route, but they don't have too many of these since a parked aircraft isn't making money, and there isn't always one of these standby aircraft readily available as a substitute (though if a defect is found in flight the replacement can be on the way before the defective one lands to reduce the delay). Meanwhile, mechanicals are typically such a localized problem that the schedulers can't get away with just delaying flights systemwide, like they can often do with severe weather. They have to run the rest of their fleet on time, and that means either getting a replacement plane to the gate, pronto, or else sending that replacement plane empty to the cancelled flight's next destination, so the new plane can get those passengers on to their destination.
Obviously, severe weather can cause major ripples through an airline's schedule for days to come. If ORD or DFW has a "ground stop" due to severe precipitation or high winds, that will delay not only the flights scheduled to arrive or depart in that time, but every flight those tail numbers were scheduled to run for the rest of the day, as well as various scheduled connectors (those connecting flights, if they're not also under severe weather, often have to depart with whatever passengers they have otherwise there will be even more delays; then the passengers who have missed that connectot will have to be rebooked, on other airlines if need be).
That delay time also counts as "active" time for a flight crew; if a flight is delayed beyond a crew's end of shift, they often must get off the plane to comply with FAA regs and union CBAs. The scheduled replacement crew, however, was supposed to get on at the next stop hundreds of miles away; so, it's not just the planes that have to be replaced on a route when a flight is cancelled. In cases of a severe delay extending beyond a normal shift change, the crew either flies the plane if it's legal and are paid overtime, or if it would be illegal for that crew to continue, an on-call crew is brought in, flies the plane to the scheduled changeover point, then rides a standby seat (or in the extreme an empty plane) back to their home terminal or somewhere else they'll be useful when their shift really starts.
All of these considerations and more are weighed by the sophisticated algorithms now used to generate flight schedules. American Airlines calls theirs the "cancellator", and when a major hub like DFW, ORD or ATL sees a weather shutdown that's pretty much exactly what it does, sacrificing flights to and from that hub and some of its connectors to try to save what it can of its passenger load for the day (and thus the airline's profitability for the quarter).

Thank you for your very detailed answer! So here's another question based on the original: how does an airline know that a specific type of plane will be operating a flight if they don't know which specific one will? Don't they need to know that one will be available at the time of the flight in order to use it on that flight?

It's easier to know the type of plane in advance versus the actual plane, because the distance to be flown along the route and the typical passenger count at each stop will call for a particular model of plane to be used. Airlines don't typically have just one or two of a model of plane; they'll buy several dozen of a model that works for a specific route type, and they'll try to replace like-for-like because that's the best use of equipment.

Now, even this isn't set in stone; an airline might have to pull a 737 for maintenance at the last minute, and run the rest of its route with an A319 instead. There are only two situations in which an airline can 100% guarantee even the type of airplane; (1) when the airline operates no other type of aircraft (e.g. Southwest; it's run only 737s for decades, though you could still get a 737-800 instead of a 737-700), or the airline has no other type of aircraft that could do the job (ultra-long-hauls, for instance, are flights that the airline may operate only one model capable of running).

Replacing a 319 with another 319 means the original crew can keep on doing what they were scheduled to do. Replacing it with a 737 means the 319 pilots now have to be replaced with 737 pilots for the next legs. Less of a deal if their day was hub to somewhere to hub, more of a complication if it was hub to A to B (overnight) to C to D to home. But you do what you have to do, sometimes.

There are many cases where a plane returned after two hours and another plane was pulled to do the flight instead and there are many cases where a plane broke long before a flight and the flight was cancelled and everybody rebooked. Which is done depends on which is easier to arrange, not on when the problem occurred.

@RalphJ - Some airline pilots have multiple type ratings, and some type ratings are valid for multiple aircraft models (though typically not between manufacturers). The 757 and 767 have identical cockpits, for instance, so if a 757 was pulled and the best available substitute was a 67, the crew could climb right in (though it might no longer be a profitable flight for the airline with that plane). It's not inconceivable for a career Boeing pilot to also have some stick time in an Airbus, but for the most part you're right; an A319 would very likely require a different flight crew than a 737.

Lots of things can require a diversion other than mechanical failure (weather is the biggie).

How far ahead they formulate their plan will vary for each airline, but plans can change even as late as hours or even minutes before the flight, in case of things like broken planes or inoperative equipment that makes a swap necessary.  Say an aircraft that was going to operate a couple of long-haul flights & overnight at an out-station develops a problem with a center-tank fuel gauge. It might get swapped with an aircraft operating shorter legs (so the center tank would remain empty) that's scheduled to overnight at a maintenance base. This would get the gauge fixed sooner, and make for fewer issues for the long-haul crews.
But you'd have a different tail number show up at your gate than was planned before the swap was put on.

Also note that the minutes before flight can come even hours after scheduled departure. It happened to me once (I'm not a frequent flyer!), that other passengers and I watched intensive service efforts on our scheduled plane for half an hour after our scheduled departure, to be moved to the neighbouring gate as soon as a replacement plane became available. The captain then apologised for the delay saying "We are going to be some twenty minutes late, which happens when you take someone else's plane."


text:
Where do I land if I fly from KLAX with a constant east heading, crossing the US and the Atlantic ocean?
Los Angeles KLAX and Casablanca GMMN (Morocco) are at the same latitude.
If the aircraft follows a magnetic 090° heading, the initial true heading will be 102° due to the declination.

(source University of Alabama.)
That means the path will start slightly southerly.
What will be the path followed until reaching a continent on the other side of the Atlantic?

If an aircraft is following a magnetic course changes in magnetic declination as the aircraft moves along its route of flight will affect the true course, and on a long flight such as the hypothetical trip posed here we need to take that into account.
Magnetic declination is empirical data, i.e. there are tables of it, and while formulas exist to approximate it you would normally use the reference tables. There are several sources of data for the worldwide declination of the magnetic field, for example here.
  Following the link "Magnetic Model maps and grids" I took D_map_mf_2010.zip which contains a simple lat/lon/declination table (0.5° steps) and wrote a small simulation which moves the aircraft 10 km along the heading, calculates & records the new angular coordinates, moves again and so on. The result is this figure:

The green arrows show the direction of north as displayed by a compass, the blue shows the direction of east.
The black line was generated by the simulation shows the true course of an aircraft with a constant magnetic heading of 90°. While it will fly over north Florida, it deviates markedly to the north over the ocean and just touches the north coast of Spain.
Note that this only accounts for the magnetic declination, since your question assumed no wind.
During a real flight the aircraft may experience unknown crosswinds, so the actual position has to be determined from time to time, and a look into the table / map shows the correct heading at the current position leading to your destination. (If the aircraft only has this map, a compass and a sextant aboard.)

So, if you have this data, you can correct the compass headings such that you fly the true course you want. However, I don't know how it's actually done in aviation.

EDIT:
Here is the code. It is written in python and gnuplot, and you will not need any programming skills to use it.
Have fun!
To answer one question from the comments:

If you carried on around the world, would you return to your starting point? I'm guessing yes as we would be following a contour of equal magnetic potential?

From the physics side, magnetic fields are not conservative and so do not have a potential. However, I think it's clear what you mean.
As long as the heading is +90° or -90°, you will end up where you started. The following figure again shows a travel from KLAX heading 90°, but with a total lengh of 40mio km (i.e. 1000 times the circumfence of the earth and a little more turns for the track as it's not at the equator)
As you can see, there is just a single black track, no deviation.
And if you want to fly to Casablanca, you will need a constant heading of 93,6°. And if you don't land there and have enough fuel, strange things happen:

I would also like to emphasize Bob Jarvis' comment, about how it's done in the real world:

Long distance journeys, whether by air or sea, will generally use a "great circle" where the heading steered is not constant. In practice the continuously changing great circle course is broken up in to a series of segments of constant heading. Reference here.

I simulated it. Looks like frog's legs instead of couscous as dinner after arrival.

Love that you programmed the solution. This is great.

Awesome answer! I made a few changes to line it up with the current state of the question, if I messed anything up let me know.

Thanks for your comments. The "tool" is just a python script written by myself out of the box. The graphs are done using gnuplot. The continents also just come from a data file from the web. If you want, I can upload a software bundle, so you can play with it. But I'll do that tomorrow, as it's 2pm here.

Based on that route it would appear that you're likely to land in northern Spain, as the continent will be insight, even if you're a couple miles off-shore. (This exercise gets a lot more fun if it's cloudy). I'm guessing LEAS.

If you carried on around the world, would you return to your starting point? I'm guessing yes as we would be following a contour of equal magnetic potential?

Long distance journeys, whether by air or sea, will generally use a "great circle" where the heading steered is not constant. In practice the continuously changing great circle course is broken up in to a series of segments of constant heading. Reference here.

Not sure if my edit triggered a notification. I've added the code and played a bit with the simulation...

@sweber The link to the code is broken. It would be great to paste the code somewhere else.

@Pere: I've put the code on my google drive - this should last longer.

Your "strange path" is basically a rhumb line, just using magnetic heading instead of true heading.  In particular, this is why it ends up at the south magnetic pole.

Finally I'm adding this update to the answer sweber provided years ago, using current magnetic declination at an altitude of 15,000 ft. It shows a larger deviation. It's not the magnetic declination has changed (at latitude 40°N, the secular variation range is -0.11° to +0.18°), but altitude is possibly a significant factor.
I used a 5°x5° grid of NOAA estimated magnetic field, and a bivariate spline interpolator. The map is from Natural Earth, and the projection used is WGS84.

Arrows depict the local 90°M heading. An aircraft flying this constant heading actually reaches the coast of France near Bordeaux, at the latitude of 45° and 700NM North of it's departure airport.
In order to reach Casablanca, the heading must be 95.8°M:

Anyway such complexity linked to a non-ideally aligned geomagnetism is almost a thing of the past, the time of magnetic heading in aviation is running out. Modern navigation doesn't need it anymore, the regulation might change in the coming years and switch to true headings as the standard (more).

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

authors: Bob Jarvis - Слава Україні

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What is the performance of a flat plate wing?
By flat plate I mean this:

Source: Physics.SE
Low performance indeed, but how much low? How would:

The angle of attack,
The speed range,
The turn capability,
The fuel consumption,
Or other significant characteristic

compare to the ones of some reference foil, e.g. a NACA 00xx?
Link to related benchmarks appreciated.

I cannot answer all your questions, but maybe point you to some facts to come closer to an answer.
Most important is the thickness of your parallelepiped - more than a few percent will just increase drag, without benefiting performance. It should be as thin as structurally possible. There are lots of model airplanes using flat plates for lift. The most popular are flying discs like that below:

(picture source)
Lift
The lift curve slope of a flat plate is the same as that of regular airfoils, complete with stall. They have a zero-lift angle of attack of 0° (obviously) and separated flow on the suction side. The maximum lift coefficient of 0.7 to 0.8 is reached at moderate angles of attack - details depend on the aspect ratio.

Your typical four-digit NACA airfoil will have a maximum lift coefficient of 1.2 to 1.6, depending on camber and Reynolds number (picture source).
Drag
Due to the missing nose thrust, the aerodynamic force vector will stand almost perpendicular to the plate's plane. It will be slanted slightly backwards due to friction, but the separated flow on the suction side means that friction will mostly happen on the pressure side. As a rough approximation, the drag coefficient of the flat plate is $$ c_D = c_L \cdot \sin\alpha + \frac{0.43}{log\left(\frac{100}{R}\right)^{2.56}} + 0.3 \cdot\delta\cdot\cos\alpha$$
with $R$ the relative surface roughness, $\delta$ the relative thickness and $\alpha$ the angle of attack. The first part is caused by the direction of the lift vector, the second part is the friction contribution and will be dwarfed by the pressure part, and the third part is an approximation for the suction along the thick trailing edge. At $\alpha$ = 5° and a lift coefficient of 0.5, the drag coefficient will already be around 0.05.
Regular NACA airfoils will have a $c_{D0}$ of 0.004 to 0.01, depending on Reynolds number, and their $c_D$ at stall is normally between 0.02 and 0.025.
Performance
From the above it is fair to assume that drag in cruise condition will easily be 4 times higher (induced drag is not affected), and the optimum cruise condition will be at a lower speed due to the higher zero-lift drag. On top, the airplane will need a bigger engine to stay airborne, which will reduce its useful load. Expect fuel consumption to increase in line with the drag increase.
The stall speed of an aircraft with a flat plate wing will be approx. 50% higher than with a proper airfoil on the wing, and drag will increase much more at high lift coefficients than usual, which translates into very low sustained turn rates and load factors.
Only the angle of attack range will stay similar. All other parameters will be markedly affected.

@ArtOfCode: I used to do multiplication with \cdot, but found that shift-opt-9 produces the same centered dot. Your edit did not change the appearance of the equation on my screen, but is this different in that other OS? Should I better use \cdot again for better compatibility?

The manual dot you add gets put in thanks to Unicode - just not all computers and browsers will support it. MathJax's \cdot is, IIRC, compatible in most if not all places.

@PeterKämpf: shouldn‘t the MachNumber be considered as well? Looking at the wing profile of a F16 or Concord they look much more like a flat plate due to the transonic aerodynamics.

@rul30: You are right; I answered only for subsonic speed.

One last note: flat plate wings work extremely well on small scale lengths, as for example in the insect world. Consider that a dragonfly can hover, perform flat turns at speed, fly inverted, and accelerate from zero to 30 MPH in a couple of seconds with two pairs of flat wings, and 250 million years +/- of selection pressure have not improved their design much.
Because a dragonfly's wings twist significantly during operation, they are not strictly speaking without camber, but anyone who has ever watched them pluck gnats out of the air cannot but be amazed at what they can accomplish, aerodynamically speaking.

Yes the Square-Cube law does them many favours.

It depends of course: laminar or turbulent flow, and at which Reynolds number. $C_D$ for AoA zero looks like this (found here)

Flat plate aerodynamics are relevant for helicopter blades and wind turbines, and measurements have been conducted over 0 - 360 deg of AoA with results that are of interest for fixed wing as well. For instance from this document:

The $C_L$ of NACA 0012 over 180 degrees shows that the real gain in lift is within the first 10 degrees of AoA, after which the airfoil stalls, but $C_L$ starts rising again after its initial stall behaviour due to flat plate aerodynamics. The 0012 profile is quite thin, and the maximum $C_L$ is reached at 45 degrees - however if we look at 10 deg AoA, the 0012 $C_L$ is around 1 while the equivalent flat plate $C_L$ would be around 0.4 (extend the sine wave graph 15 < AoA < 170 to zero).
$C_D$ follows a similar pattern, again showing large gains until stall occurs and then continuing according to flat plate aero. at 10 deg, $C_D$ is barely above zero instead of the 0.12 value obtained when the sine curve is extended.

So the NACA profile has a much higher lift for a much lower drag than an equivalent flat plate. In order to get to a $C_L$ of 1, the AoA of a flat plate needs to be 30 deg instead of the 10 deg of the NACA. At 30 deg, $C_D$ of the wing is 0.6 instead of the 0.02 of the NACA, 30 times higher! So turn rate and other parameters are only of interest if the engines can deliver 30 times more thrust.

Your comparison makes the flat plate look worse than it is. It reaches its optimum at a lower lift coefficient, so the comparison at c$_L$=1 is misleading. This is not to say that a flat plate is not a poor choice for subsonic aircraft - it certainly is.

Yes good point for the cruise, although it would make for much higher landing speeds if we can't get to $C_L$ of 1.

yes, or you use a much bigger wing.

The answers already provided discuss aerodynamics in some detail.
One other significant characteristic not so far discussed is structural integrity. In a structure like a wing, there will be trade-offs between strength, thinness and lightness: the more you have of one, the less you can have of the others.
By the time you're dealing with very thin structures, then even choosing stronger-but-heavier materials won't help enough to be useful in a wing that has to support an aircraft in the air.
Even if a flat plate wing had advantageous aerodynamic properties, its structural weaknesses would rule it out of many applications.

The wing of the F104 Starfighter was pretty flat.

Flat is not the same as thin! A cube has only flat surfaces.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Jet engines: are they owned by the airline or just rented?
For commercial jets, the engines are complex parts of the aircraft, are the most expensive components, and must be carefully maintained.

Source
When a company buys an aircraft, do they also own the engines, or are they still the property of the engine manufacturer? What happens when an engine must be exchanged?

Please see here for an answer already on ASE.

What does the gratuitous image add to the question? If one isn't aware of what planes look like, this isn't the appropriate place to be teaching them.

@Nij: "If one isn't aware of what planes look like, this isn't the appropriate place to be teaching them". Actually it is.

This question is about owning engines. It has nothing to do with what planes look like. Again, not appropriate and gratuitous.

These days, engine manufacturers are not any more in the business of selling engines, but selling thrust.
Rolls-Royce were the first to offer this, and today most Rolls-Royce engines send telemetry data to four centers, the biggest one in Derby, in Great Britain, where every engine is under surveillance. An inspection can be scheduled at or spare parts can be directed to the right destination even before the pilots or the airline know that one of their engines has a problem.
By now, 80% of Rolls-Royce engines are sold at a loss which is recouped by a hourly fee paid under the TotalCare (.pdf!) program, and that center in Derby is monitoring maybe 4000 of them at the same time. Rolls-Royce has accumulated a treasure of engine operations data, which enables it to consult airlines on best practices. This makes it very hard for a third party to steal maintenance business from Rolls-Royce. All maintenance cost is covered by the TotalCare fee which now accounts for more than half of Rolls-Royce's revenue.
GE and Pratt&Whitney have similar programs. In GE's case, it is called OnPoint, sold as "Power by the Hour". The airline does not pay for the engines, but for the time they are flying. Now the engine manufacturer has a strong incentive to improve the reliability of its engines, but also a strong lever to push out third-party maintenance providers.

@Blarg for Flight 370 they did and it was reasonably well reported - a lot of what we know was derived from careful analysis of the Rolls Royce data. For the recent Air Asia incident if such data exists it will doubtless be looked at by the investigators.

@blarg: The engine performance data would be unlikely to give location data other, perhaps, than altitude data. It is likely that the distance travelld could be worked out giving a maximum search radius from last known position but turns, etc., means that the plane could be anywhere in the circle.

Does someone know how exactly the Rolls Royce engine telemetry data reaches these data centers? Do they have entirely separate communication channels, or does Rolls Royce work with the aircraft manufacturers/airlines to transmit this data?

@cwoebker: They use satellite links. If you ask properly instead of in a comment, your chances of getting a better answer are vastly improved.

The engines are owned by the airline or aircraft owner.  Whether you are talking about airlines or private jets the cost to overhaul an engine is quite significant.  Several million dollars.  As mentioned above there are different engine programs depending on the manufacturer of the engine.  For business jets there is also a company called JSSI that provides an alternative to manufacturer engine programs.
When a person or company buys an aircraft they need to look if the aircraft is on an "engine program" - if they are looking at a private jet with an engine program and one without one they really should evaluate the cost of adding the jet to an engine program to compare the price and the value.  Our site jetlistings.com lets you do a Private Jet Search and filter our aircraft that are on an engine program.  This enables an aircraft buyer to see if an aircraft's engines are covered.
An Aircraft buyer also need to figure into their budget that the the engine program also has a monthly fee based on how many hours the aircraft flies and they usually have a minimum number of hours payment for aircraft that may not fly much.


text:
What is supposed to prevent a commercial crew from flying to the wrong airport?
Context
Obviously:

Crews are skilled and well trained.
In a crew of two, one can fix others confusion.
There is a flight plan, ATC can inform of a deviation.
GNSS / ILS / VOR / DME frequencies and distances increase situational awareness.

But still:

February 2014: "Planes landed at wrong airports 150 times over 2 decades".
March 2014: Security Alert, NTSB reminded pilots to take care of not landing at the wrong airport.

After having posted this question, I did an additional research, to find NTSB came back to this problem recently, in May 2015:

NTSB releases two recommendations to FAA. One for ATC clearing to land, the other for software detection of wrong location.
Related article: "After 5 planes land at wrong airports, the NTSB has a few words of advice for the FAA".

Relatively few errors, but consequence could be tragic
150 approaches or so wrong are a very small fraction of the many millions of flawless flights, however the NTSB emphasizes the consequences could have been tragic, e.g. if the erroneous airport didn't provide the expected runway length.

Questions

Did the analysis of these incidents show distinct patterns in their occurrence that could be prevented by different procedures or different navigation instruments?
Did the involved pilots, or other professionals think specific improvements had or still have to be made to avoid recurrence?

Some common sense!

7.5 times a year seems shockingly low considering that there are something like 29,000 airline flights a day just in the US.

Very true, @egid, but each one makes for some great headlines!

This question is not useful for helping anybody understand aviation. Consider asking "what's supposed to prevent cars from being accidentally driven off the road into large crowds?"  (happens rarely, but BIG headlines when it does!) Or "what's supposed to prevent cooks from accidentally giving all their customers food poisoning?"  (same rare/headline deal applies).  The interesting question is in the one in a million (+/-) cases, what happened that a crew made the mistakes they made, missed the navigation cues, & wasn't alerted by ATC? That's very specific to each occurrence, though.

@RalphJ: The first question is: "Did the analysis of these incidents show distinct patterns in their occurrence that could be prevented by different procedures or different navigation instruments?". That is similar to your point I think.

8/12 hour rule?

According to the Wikipedia article on IFR:

VFR is the most common mode of operation for small craft. However, it is only safe to fly VFR when these outside references can be clearly seen from a sufficient distance; when flying through or above clouds, or in fog, rain, dust or similar low-level weather conditions, these references can be obscured.

So basically, a pilot would land at a wrong airport due to one of the following conditions:

He/She did not have previous experience of landing at the said airport
He/She paid more attention to VFR that IFR (which is usually suggested), and the proximity of the airports confused him/her

Any aircraft operating under VFR must have the required equipment on board, as described in FAR Part 91.205[5] (which includes some instruments necessary for IFR flight). VFR pilots may use cockpit instruments as secondary aids to navigation and orientation, but are not required to; the view outside of the aircraft is the primary source for keeping the aircraft straight and level (orientation), flying to the intended destination (navigation), and not hitting anything (separation).

This means that a pilor following VFR can get confused, and that would be a completely manual error. To prevent this from happening, he/she should raise a flag with the Control Tower before landing if his IFR shows a different destination, when compared to the place he is intending to land at following VFR.

Good answer; There are sometimes notes on sectional charts saying "don't confuse this airstrip with this other one" when the confusion has been common among even experienced pilot, but airliner pilots typically aren't flying by paper charts.

It sounds like you are using "flying IFR" to mean "paying attention to electronic aids to navigation"-- as ipposed to using "pilotage"-- but that's not what it means.

Some of them are inexplicable, like the Dreamlifter 747-400 that landed at Jabara airport in Wichita, instead of McConnell Air Force Base. The aircraft REQUESTED and was issued the RNAV 19 approach, and stated it to the ICT controller, who then cleared the aircraft to land.
VFR conditions, at night.
Although this seems reasonable enough at first, I have to wonder how the pilots could confuse AAO (with its medium intensity lights) with IAB, which has high intensity lights with sequenced flashers (not to mention a LOT more runway lights).
The NTSB suggested that the controllers should tell the pilot about the other airport. Why should they? The aircraft was on a published approach!

Normally you will never land at the wrong airport if it is towered because you make an announcement. So, for example, the pilot might say something like "Norwood tower Fedex123 ten miles out on two six zero with information Juliette". Then the tower might say something like "Fedex 123 please ident", then you ident. Then the tower might say "I have you 25 miles out on three one zero". Then you know something is wrong. If the tower does not answer at all that is another sign something is wrong.
Once I started to land on the wrong airport. I was flying into Nashua Boire field (KASH) from the north late at night. At that time the tower was closed at Nashua, so I was just announcing on CTAF which goes unanswered and that is normal. I see the runway, line up and am coming in, when WHOA! a big Embraer slides in right below me. We had plenty of separation, but nevertheless I am like, "What the hell is an Embraer doing here?" The answer, of course, is that I was not landing at KASH, but at Manchester, a much larger airport directly north of Nashua. In the darkness one runway looks like another.

Wasn't there a case when a tower cleared a plane to land on a different airport?

This was hilarious to.. http://news.aviation-safety.net/2014/01/15/tanzania-aib-details-ethiopian-boeing-767-wrong-airport-landing-incident/

IFR pilots—which is all airline flights—rarely report position, because they are under radar control all the time. The controller should normally notice the aircraft is not on the usual approach path, but if they are busy, they can miss it.


text:
Why are many jet aircraft designed to cruise around FL350-370?
If the flight distance permits, the B737-800 will cruise at FL350, the A320 a little bit higher...

Flying at FL370. Photo: Live from the Flight Deck by GolfCharlie232 (reframed)
Elements such as time to reach cruise altitude, engine and airframe efficiency at this altitude, and acceptable cabin pressure surely influence the choice, but:

What are exactly the important criteria used, and the compromises made by engineers?
Would engineers choose other altitudes if the technology or any other current limits could be improved?

There are multiple factors that affect an aircraft based on its cruise altitude.
The cruise altitude directly affects the aircraft pressurization and aerodynamics. In order to keep the cabin altitude around 6000 to 8000 feet, the fuselage would have to withstand a higher pressure differential. This would require more material, and make the plane heavier. Newer materials used on the 787 and A350 handle these loads better, which allows a higher pressure differential and larger windows.
The altitude also affects the aerodynamics. Aircraft typically cruise at a certain Mach number at high altitudes. The indicated airspeed for a certain Mach number gets lower with higher altitude. This can result in lower drag, but poses challenges as the airspeed drops lower. See: What determines the maximum altitude a plane can reach?
Also, see the answer by Peter Kämpf for more detail about the aerodynamic aspects.
At higher altitudes, less air is available for the engines, reducing the available power. Along with this there are efficiency benefits. See: Why do jet engines get better fuel efficiency at high altitudes?
As the answer by Ghillie Dhu explains, those benefits stop increasing around FL360.
The lack of breathable oxygen and increased pressure forces on the fuselage caused by the lower air pressure also lead to greater risks, resulting in tighter regulations on aircraft intending to fly higher. These regulations will add additional cost to flying higher, affecting decisions on service ceilings.
§ 25.365

(d) The airplane structure must be designed to be able to withstand the pressure differential loads corresponding to the maximum relief valve setting multiplied by a factor of 1.33 for airplanes to be approved for operation to 45,000 feet or by a factor of 1.67 for airplanes to be approved for operation above 45,000 feet, omitting other loads.

So for planes operating over 45,000 feet, the structure must be able to withstand an even higher pressure load factor.
§ 25.1441

(d) The oxygen flow rate and the oxygen equipment for airplanes for which certification for operation above 40,000 feet is requested must be approved.

Planes operating over 40,000 feet must get special approval for the oxygen system.
§ 25.841

(2) The airplane must be designed so that occupants will not be exposed to a cabin pressure altitude that exceeds the following after decompression from any failure condition not shown to be extremely improbable:
  (i) Twenty-five thousand (25,000) feet for more than 2 minutes; or
  (ii) Forty thousand (40,000) feet for any duration.

The cabin altitude is not allowed to exceed 40,000 feet under any condition that isn't extremely improbable. The higher the plane flies, the more difficult this will be to certify.
Business jets tend to have higher cruise altitudes, because the smaller structure is easier to reinforce for higher pressures, and typically sees fewer load cycles. Efficiency is also not as important as speed and comfort, so some weight can be spared for the stronger fuselage. The higher altitude also affords more flexibility in routing since most other traffic including commercial airliners are cruising at lower altitudes. Business jets may also be certified under less-stringent regulations.

Just to be clear, by staying under FL400 it's basically impossible for condition (ii) to occur, right?

@fooot Yes, but above FL180 everyone switches the altimeter to standard (29.92), so you are always (if you're following the rules) flying at the same pressure altitude regardles of what the weather is doing - all flight levels above FL180 are therefore always pressure altitude.  The values in 25.841 are pressure altitude for that reason (it makes the air density a constant, which is what you're worrying about when you're trying to breathe).

-1. Peter's answer seems to show that cabin pressure engineering is less important than aerodynamic considerations. Secondly you spend a lot of time talking about the regs, but I doubt the regulations came before the practice. (We don't fly at FL350 because of the existence of regulations; the existence of regulations happened because we fly at FL350.)

A380 is approved for 43,000ft and 1 minute of exposure to atmosphere before the aircraft must be pressurized or below at least 40,000ft.

In case of rapid decompression, the cabin altitude will increase to FL400 if the aircraft is actually flying at or over FL400. And since no aircraft can dive to a safer altitude instantly, the occupants will be exposed to a cabin altitude of >40,000 for some duration, violating (ii). Does that mean regulations effectively bar ANY commercial aircraft from flying over that altitude no matter what? Or is rapid cabin depressurization considered "improbable"?

In a word, the tropopause.
Gas turbine engine efficiency improves with colder & denser air. As an airplane climbs through the troposphere, the density & temperature both drop, and the loss of density is more than offset by the lower temperature. Above the tropopause, however, the density continues to drop while the temperature holds (approximately) constant.
In the U.S. Standard Atmosphere model, this occurs at 36,089 feet. This represents a local (possibly global) optimum altitude for efficiency (and if there is a better optimum at a higher altitude, it's inaccessible for other reasons).

But denser air would also be associated with greater drag, right?  So you might want to fly even higher than 36,089, because the reduced efficiency of the engine could be offset by the reduced drag.  I believe there are airliners that routinely cruise at 40,000 or 41,000 feet (I often fly on 737-700 and 41,000 is usually the cruising altitude announced by the flight crew, if I recall correctly).

Yes, but you lose lift with lower density as well; L/D is unaffected. To some extent, off-peak efficiency at higher altitudes is worth the cost due to less traffic (i.e., more direct routing); you might burn more fuel per time, but the total fuel burn gate-to-gate could be reduced.

Between -30° and +30° latitude, the tropopause is at about 50,000 ft.

I know there is already an accepted answer, but some key facts are missing.
Mainly, the optimum cruise altitude is where thrust and lift requirements for both take-off and cruise balance well. An additional benefit is the cooler air which increases the efficiency of heat engines.
With increasing flight altitude, the airliner needs:

Bigger engines to create the needed thrust in thinner air
Bigger wings to create the needed lift

With the wings, the size of the tailplanes will also grow; this effect alone likely will weigh more than the beefing up of the fuselage structure for the increased cabin pressure. Flying higher will make almost all parts bigger and heavier.
Note that Mach 0.85 is a hard limit for efficient flight; airliners cannot compensate for lower density by flying faster. The only way to allow higher flight levels is to attach bigger wings and tails.
Another consideration is Breguet's formula: Jet aircraft have their optimum cruise lift coefficient at a value of $c_L = \sqrt{0.6\cdot c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$, if we assume the thrust of high-bypass-ratio engines to vary with speed proportional to $\text{v}^{-0.5}$, which is a reasonable assumption. This means the airliner cannot fly higher by flying at a higher lift coefficient: This would decrease efficiency.
(Nomenclature: $c_{D0}$ = zero-lift drag, $AR$ = wing aspect ratio, $\epsilon$ = span efficiency, v = flight speed)
With the wing size and the engines needed for flight at Mach 0.82 in the tropopause (Mach 0.85 is really not as efficient; follow the link to find out why this is the quoted cruise speed for long-range airliners), the take-off distance is quite reasonable and approximately matches the airports which had been defined by NATO during the cold war. Flying any higher into the stratosphere would increase the aircraft's mass due to bigger engines and wings, but would not incur the efficiency gains of increasing cruise altitude in the troposphere, where temperature drops with altitude.
Conversely, picking a lower design cruise altitude would allow to make both wings and engines smaller, but this would translate into:

Higher take-off and landing speeds, and critical speeds during take-off due to the smaller wing,
Lower take-off acceleration due to smaller engines,
For twins: Not enough thrust during take-off when one engine fails,
Lower climb speeds, so it would take longer to reach cruise altitude, and
Not fully taking advantage of the cold air up in the tropopause.

Designing for a lower cruise altitude would translate into much longer runways and less efficient flight overall.
Designing for cruise in the tropopause is simply the sweet spot for airliner designers where all conditions match well and produce a balanced outcome.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What should a pilot do if none of the control surfaces are responding?
What would a pilot do if none of the control surfaces are responding?
For example, a pilot flies a medium-sized plane and to make the situation a bit less hectic, they're the only one onboard. Then they make a subtle turn, but nothing moves. They try again, but the plane isn't turning. They then become quite worried and assess the situation, trying if any of the control surfaces are working. To a shocking realization, none of the control surfaces are responding. And luck isn't on their side: when the control surfaces stopped responding, the plane was at a slight descent of about 5 degrees. If they can't figure out what to do soon, they're going to collide with the ground. The pilot can't tell what is causing the problem but assumes that it is something wrong with the control surfaces themselves, not the control linkage between the control surfaces. The pilot can't tell if the control surfaces are frozen, stuck, or broken. And the final take is that the plane isn't going slow enough for the pilot to safely bail out of the plane. They guess that they have at most 8 minutes before they crash.
So what would the pilot do? And if it seems highly unlikely that such an event would ever happen under the given circumstances in the example provided, then imagine a significantly different scenario in which a pilot is in a P-51 Mustang and they've been shot all over (the plane, not the pilot) to the point where nothing is working, likely linkage failure or other damage. What would a Pilot do, especially if they're in a situation where bailing the plane just isn't an option?

Why are they descending? Is the engine out too? One engine or two?

Nope. No engines are out in the example. Say, there was some dark, suspicious-looking clouds and the pilot didn't want to go straight through it, and so the pilot put it into a minor descent to go under the cloud. Just an example.

A stuck control surface acts differently from one whose linkage got disconnected.  For example, an aileron will float up.  Also, if it's not fly by wire, a stuck surface feels completely different at the stick (or pedals) than a broken linkage.

Even in a war, how could all surfaces fail at the same time?  (This doesn't sound like airliner hydraulics or FBW with total electrical failure.)  The pilot would surely notice the first one failing before the others failed.

United 232 springs to mind. But this feels like a very artificial, 'movie plot' scenario, and I'm not sure what sort of answer you expect. Are you asking what practical troubleshooting steps the pilot might take?

@Pondlife yes, I'm asking what a pilot should do in such a situation.

Not that it changes anything, but I'd point out that 5° descent is not "slight": it's a lot. A "slight" descent, say 100-200 fpm, would be of the order 1:100, which is a fraction of a degree; perhaps just over a degree for a slower airplane. Landing (final approach) is conducted at about 3°.

The exact outcomes depend on too many factors for a meaningful answer, in my opinion. What exact systems have failed? How have they failed? What systems is the aircraft equipped with? This is like asking how you should deal with a broken steering wheel without specifying if you are in a golf cart, Formula 1 car or a Bagger 228.

Hopefully while this is happening, the airplane is in trim and more or less wants to continue where it's headed.
Say the airplane was in trim at 150kt and you had power set for level flight at trim speed. If the trim system still works, you still have significant pitch control, because you can vary the speed that airplane wants to fly at and you have power that you can adjust to make it climb or descend.  You also have flaps which change trim significantly and if there are people in the back, you can alter trim speed by getting them to move forward and aft.  If the trim system doesn't work, all you have is flaps and C of G shifting if you can, and the effects of power changes to the extent they are there.
The big problem isn't pitch, it's roll control. If you're in a single engine plane and have no roll or yaw control, you are pretty much screwed. Once the airplane gets disturbed and starts to drift off into a spiral, you're done without some way to roll the wings level.
If you're in a twin, with engines on the wings, you might have a fighting chance because you can achieve some control over bank by using differential power to skid the plane, which makes it tend to bank toward the "slow" side, depending on how strong its roll-yaw couple is.  Jets with swept wings achieve really high roll rates when skidding, so differential thrust can be used to control banked turns with reasonable precision, although the input/response loop is very slow and would require a lot of finesse to avoid getting into self-magnifying oscillations.
A straight wing twin with mild roll due to yaw would be pretty challenging and the change/result cycle would take forever. So hopefully the air is smooth while this is happening.  If it's really bumpy, you're probably screwed.
So it that happened to me, and I was in a twin, I'd be experimenting with asymmetric power, trim, flaps etc., to see what I could do, and to the extent I was able to gain some control, I would spend as much time as I could practicing before I tried to descend.  Then the main thing is to find a very large and long runway to land on, knowing the probable result is a hopefully survivable crash.  If I auger straight into the ground, because all the slithering and sliding from power changes meant that I wasn't able to maintain control, well, at least I went down fighting.

Alternative roll control :)

@Sanchises Exactly what I was thinking of.

I was thinking of that also and I'd probably try it myself out of desperation, but you'd have to be in something like a 172, and I don't think you'd have to body strength to shove and hold panels out sufficiently to get any control.  I've you've ever tried to push a door on a 172 open while at any flying speed, it's pretty tough to get it out more than a few inches.

Most pilots would go through whatever procedures they could to free up the controls, including improvising or forcing things.  After that the only thing left is to perhaps attempt some sort of spiritual reconciliation if they are moved to do so.
Pilots face death the same way other mortals do...

There have been cases like this. One of the most successful incidents occurred in Baghdad when DHL A300 was shot with a manpad.
Airbus has published a neat study of the case with analysis. Basically AC will enter a long, low frequency phugoid oscillating around trimmed speed. You forget the speed and fly the pitch with thrust.
https://www.smartcockpit.com/docs/Baghdad_A300_Incident.pdf

The OP mentioned engines out in the comments.


text:
Can a person legally mount a fake gun on an amateur-built aircraft?
Is there an FAA rule that states that no amateur-built aircraft are allowed to have a weapon mounted to it? (If so, I'd certainly like to see this rule and its conditions) Say I want to build an airplane that a friend and I made blueprints for a while ago, and it was about 60% fantasy. But the plane doesn't look the same without the guns. The guns really add a different feel to the plane, and to have no guns makes it feel as though it's missing something. But clearly I'd never use it. I just wanted to know if it is even legal to put a gun on an amateur-built aircraft,  which I'd assume it isn't. So to avoid any trouble, I think it'd be best not to put any functioning guns on my plane. So, this begs the question, Is it legal to put a fake gun on an airplane, or to put a functioning ball turret that has fake guns?

Empirically, yes it's legal. I've seen several reproduction WW1 aircraft myself at airshows with fake guns, missiles or bombs attached. And I was once at an EAA chapter meeting where a member demonstrated his fake gun 'firing' using compressed air. There are also factory-built aircraft with fake weapons added later, by the way.
As to regulations on this, I've never seen one. Typically US laws and regulations state what you can't do, not what you can do. For example, there is a law that prohibits attaching dangerous weapons to drones.

So does this mean that I can put it on my own plane?

If it's legal to add it to your plane.  If you have a homebuilt you can pretty much do what you want within reason, so knock yourself out; if it's a certified plane, you'll have to get an approval as a one-time mod or STC or similar.


text:
How and why can multiple people control the Boeing B-29?
I am making a down-to-the-1/128th-inch (literally, to the 1/128th inch) model of the Boeing B-29 Superfortress in SketchUp. Starting from zero, I had to make the entire plane up, and to be honest it looks exactly like the real thing at this point. I went down to copying every detail in even the dials and switches and levers, and realized something.
I saw that the pilot can control each of the 4 engines independently. Now, that isn't exactly the problem. The problem, is that the Pilot, "Second Pilot", and Flight Engineer can all control each of the 4 engines. And I can't figure out how that's supposed to work! I mean, can the flight engineer just turn up the throttle whenever? But what if the Pilot is going to speed up so that he/she can reach a higher altitude, but the flight engineer doesn't know that and so he turns the throttle down to decrease engine heat because the cowl flaps are at max degrees for stable flight?
Then there's the issue: If the flight engineer turns the throttle down at the same time that the pilot turns it up, what will the engines do? And I doubt the pilot would speak his every move to the "Second Pilot" and the Flight Engineer to prevent a mix-up. So, does the Flight engineer have to literally request permission and state his/her reasoning to the Pilot before changing the throttle?
And then I thought some more, and realized that the "Second Pilot" also has a "steering wheel", which I know for a fact that other co-pilots have in other planes, but I never knew why. The Pilot can handle the plane's steering by himself/herself, can't they? And even if they couldn't, giving the "Second Pilot" a steering wheel too... well, I can't see how that fixes anything. And if the "Second Pilot" turns the steering wheel at the same time that the pilot does, what does the plane do?
Same thing for the pedals I realized that the Pilot and "Second Pilot" both have. It makes no sense. I get that the "Second Pilot" could take control of the plane if needed because of these duplicate control instruments, but what would happen if they were (accidentally) used a the same time as another? And I also don't get why the Flight Engineer would need to be able to change the throttle. The Flight Engineer literally sits in the opposite direction of the front windows, so it isn't like Boeing wanted the Flight Engineer to be able to fly the plane.
Any suggestions would be very helpful. And, sorry about the gigantic question.

Teamwork, training, clearly defined roles under a common mission, communication - all lumped under what we now call Crew Resource Management (CRM).  Really though, you should try to focus your question on one or two specific areas.  Because it is a bit messy now. (Like you just puked up misunderstanding...)

It's not just the B-29.  Pretty much every plane that carries more than a single person has dual controls.  Most can stay aloft for many hours - the B-29 for roughly 25 hours in ferry mode.  Suppose your pilot needs a bathroom break or a nap, or gets shot in combat?  You'd really like someone else to be able to fly the plane, wouldn't you?

"to the 1/128th inch" are you taking into account thermal expansion/contraction of the material?

Also, war. Any one of those stations could turn into a smoking crater, and it would be really nice if the plane could still be flown even if the main pilot's chair is falling towards Dresden.

Look up the Air France 447 crash, caused in part by invalid dual control inputs.

Just one point, you may absolutely know this already.  if you're doing this Blender exercise as a hobby, fantastic.  But do be aware you can trivially purchase (for the odd hundred bucks) such a 3D model.  The usual industry marketplace is http://turbosquid.com

@EarlGrey No, actually. Funny suggestion, though. I never thought about that. But I'm actually only modeling down that tiny based on Military Blueprints and other data, which I'd suppose are going to be the equivalent of the plane being at normal temperatures on the ground.

@Fattie I'm doing this on SketchUp, not Blender. And another thing, is that such a B-29 does not exist on the 3D marketplace. I have looked, and I found models of "shells". This means that the Model is Okay on the outside, but empty on the inside. I found only 1 model with an interior, but the interior was horribly inaccurate and the dials were images of dials, not physical dials. And the images were of a common passenger plane, not  the B-29's dials. So I decided to make my own, as detailed as possible.

hi @wasabi !  I googled "B-52 3D model" and immediately found many; however I appreciate you mentioning you want interiors too! I do have some serious advice for you.  I don't know if you wanna hear it!  "SketchUp" is not a serious tool.   It will take you maybe 2, 3 hours to change to using a serious tool (Blender is great, and free).  Versus the 100s of hours to achieve your goal.  I would respectfully suggest you just forget about SketchUp and switch to Blender, if not Maya.  You are facing an enormous task, best of luck!

btw the Blender site on this network https://blender.stackexchange.com is incredible, @Wasabi  All the best

@Fattie lol, I'm making a B-29, not a B-52.

heh sorry good one @Wasabi  !   I surely hope you download Blender for that enterprise

to be technically correct during the bomb run, the bombardier or rather the bomb sight, flew the plane guiding it through an autopilot type control adjusting the flight path of the plane as the bombardier adjusted the sight. So 3 people could fly the pane, pilot, copilot, and bombardier while 3 people controlled the engines, pilot, copilot, and flight engineer.

In aircraft of this vintage, all the controls are mechanically interconnected.  If the left-hand pilot's control yoke/ wheel moves, so does the right-hand pilot's.  Likewise for the rudder pedals.  And if a pilot or the flight engineer moves a throttle lever, the other throttle lever for that engine will also move.
If several people are exerting different inputs on the same control, then-- "strongest man wins!"
But normally the crew would have an understanding, at any given time, as to which pilot would be flying the plane, and who (which pilot, or the flight engineer) would be controlling the throttles.  Standard protocols would be established, and reinforced via training.  Normally only one pilot would be "flying", i.e. handling the primary aerodynamic controls (aileron, elevators, and rudder, via the control wheel and the rudder pedals), at any given time.  Normally the flight engineer would handle the throttles on this aircraft, in accordance with whatever requests the pilot flying the plane made via the intercom.

So, if the flight engineer moves a throttle lever and the pilot catches his lever ghostly moving down and he doesn't want it to move down, he tries to bring the lever back up again, the flight engineer feels the tension and resistance as if someone is trying to stop his lever from moving, and so the flight engineer ceases to move the lever; or something like that?

@Wasabi -- see expanded version of answer

Ah, I see. That makes sense. And just another thing, before I resume making my B-29 in SketchUp, what does "Manifold Pressure" mean? I know what "Pressure" means of course, and what "Manifold" means, but is the dial referring to the cylinders? Because on the flight engineer's wall of dials (literally, it is a big wall covered dials, and I have to replicate every single one), there is only 2 "manifold pressure" dials, not 4 like there would be if "Manifold" was for the cylinders in each engine. Oh, and I noticed that there are 2 climb/descent dials, and one is labeled "cabin". Why is that?

re "there is only 2 "manifold pressure" dials, not 4 "-- no idea why this would be, seems like there should be 4.  re "and one is labeled "cabin""-- rate of change of apparent altitude inside plane, i.e. essentially rate of change of cabin pressure?  (The B-29 was pressurized.)  Just guessing.  But, we're really not supposed to use comments for too much discussion on ASE...

If it won't harm anything to put links in a comment, here are the links to the 2 images of the wall of dials that I am looking at: https://media.defense.gov/2015/Aug/17/2001273172/-1/-1/0/150817-F-IO108-004.JPG and https://media.defense.gov/2006/Aug/29/2000544420/-1/-1/0/060829-F-1234P-014.JPG You'll probably have to copy + paste them into a search bar.

And as you could probably see, there is only 2 "Manifold Pressure" Dials.

Could be grounds for two more questions-- I'm sure someone will know the answer--

Some of those engine gauges have two needles (one long one short), likely representing inner engine and outer engine.  So you can show four engines on two gauges.  Hard to see that with them all sitting on zero, you have to look really close.  It shows up best on the "oil pressure" gauge on the far left side of the photo.

Ah, smart. I just realized that the needles visible for the first dial says "4" and for the second, "2". I know that the dial wall follows an order of engines dials going from left to right: 4, 3, 2, 1. And so the first dial is to the left while the second is to the right, and the fact that the second dial's needle says 2, skipping 3, means that the first and second dials both have 2 needles, but because the plane is no longer flightworthy (that flight wall is of BocksCar, not FiFi), the needles are at base position, meaning that the second needles are hiding behind the first needles.

Actually it appears that there are eight oil pressure needles in all (two needles each on four gauges) -- why that would be I have no idea-- might make a good second question-- not all the same redlines etc-- two different oil systems per engine?, something to do with props, or superchargers, or ???

Further to your "strongest man wins" with the purely mechanical linkages, there are cases (combat damage, extreme weather) where both pilots have used their strength together to manhandle the controls in adverse conditions where one pilot on his own was not strong enough. Also as far as controls go, the autopilot could take over control of the mechanical linkage - and in turn, the bombardier's fine-adjustment controls overrode the autopilot guidance.

Quiet flyer is right, here are some more comments to help.
The Pilot In Command (PIC) will advance the throttles for takeoff. The flight engineer's job is then to follow with setting the mixtures and the prop pitches while monitoring oil temps, manifold pressures, head temps and RPM's.
During the climbout, the flight engineer will continually adjust mixture, prop, throttle, cowl flaps and (possibly) turbo wastegate as altitude is gained, according to the published values, and monitor oil pressure & oil temp, and head temperatures.
When the PIC declares achievement of planned altitude, the flight engineer them looks up the book values for cruise at that altitude and ambient temperature and adjusts the aforementioned controls as called for.
If the PIC elects to establish a descent, (s)he will pull back the throttles and the flight engineer then follows up with the appropriate prop, mixture, and wastegate to keep the engines within limits.

To actually answer the question: the three different positions in the B29 could control the B29 engines at any time to a degree. The flight controls could be controlled by any one of the two pilots at any time. The point is however that they did not randomly do this.
I might add a few random thoughts to the answer here. My background is from a long-time ww2 flyer fan (if you can say such things) and as private pilot in single engine airplanes (Cessna 172 being one example).
First, the crew of a bomber has a single purpose and is trained together. A well-functioning crew will not fight for control. Instead they have different roles during different parts of the flight. American bombers had two pilots; English bombers had only one pilot (someone else could perhaps describe the history of this). It sure is simpler to learn to fly an airplane if there are double controls for two pilots (I remember well my first flight in a PA36 that has only one pilot).
The syllabus used in training, as well as later, is that one pilot is flying, being pilot in control or short PIC. When I learned flying the wording was "You are flying" / "I am flying". During training / learning to fly, the instructor would say "you are flying" and I as a student would be controlling the plane.
This continues into larger planes with two qualified pilots: each pilot had and has different roles in the different phases of flight.

Short digression: phases might be as example engine start, warmup, rollout, liftoff, rising, stable flight, deplaning, landing (and so on).

The "pilot-not-flying" might call out heights and speeds and items on the checklist, while the PIC would manipulate the actual flying controls. They work as a team, not as competitors.
Generally, today, large planes have two pilots. Most of the other stuff is handled by the computers. In the B29 days, you needed a third member of the crew, the engineer whose responsibility was to "pamper" the engines, to keep track of and move fuel between the multitude of tanks (the B29 in basic configuration had 11 tanks and you had to manually select to pump fuel between them) and such things. The engines in the B29 additionally had quite a few controls that had to be handled correctly; examples are cooling flaps, superchargers and compressed air for the cabin, propeller settings, fuel settings and so on. I believe that once a stable flight situation was in place (such as en-route), the engineer would be responsible for synchronising the propellers to the same speed and generally keep the engines happy, including monitoring pressures and temperatures and adjusting to the current flight level and outside temperature. This third position, the flight engineer, continued well into the jet era with the early 747-s having that as required crew member.

The British WWII heavy bombers varied. The Stirling, which was derived from the Sunderland, a long-range patrol flying boat, had dual controls and a flight engineer. The Halifax and Lancaster had only one pilot's seat plus a flight engineer. Since many aircrew were men who'd washed out of pilot training, there was normally at least one who could fly the aircraft.


text:
How are spacecraft and aircraft traffic coordinated?
From time to time spacecraft cross our atmosphere, either climbing to space or returning from space. While the probability for a collision is tiny, it is certainly not null, especially during reentry, when the trajectory is not vertical and can cover hundreds of kilometers at aircraft altitudes.
Is there any coordination to prevent collisions between spacecraft and aircraft?

Related

A TFR will be issued for the area that the spacecraft is expected to need for safety. Here is an example.

No pilots may operate an aircraft in the areas covered by this NOTAM (except as described).

No exceptions are described, and the airspace is patrolled (at least for manned launches). As with errant sea vessels, a launch may have to be scrubbed if the safety area is compromised.
The company or agency in charge of the space flight operation would need to contact the FAA to coordinate such a TFR.
For space shuttle landings, Special Use Airspace was established. The shuttle landed in a pretty steep profile, so it only spent a relatively short time in controlled airspace. ATC coordinated directly with NASA while the shuttle was transiting the airspace.

What about something like Apollo 11? It splashed down in the middle of nowhere, about 250 miles south of Johnston Atoll. Does anyone even have jurisdiction to say "No pilots pay operate an aircraft" there?

Also, your answer is very US-specific. I doubt the Roscosmos co-ordinates with the FAA when they're launching something from Baikonur. ;-)

@DavidRicherby great points

@DavidRicherby over international waters no country has the authority to say "no aircraft may operate here", but they can issue NOTAMs and activate Warning Areas, which effectively say "it would be a bad idea to operate your aircraft here, and don't say we didn't tell you".  Each country can also bind flights operating under their flag to respect all countries' warning areas, and most do. And they can issue suitable clearances to traffic operating IFR in their oceanic FIRs (i.e. ~all civil transoceanic traffic). See also ICAO.

@DavidRicherby: Besides the other, few people are silly enough to mess with the airspace claimed by an aircraft carrier without a really good reason.


text:
What are the practical impacts of airports in the US being mostly IATA Level 2?
IATA classifies airports using levels, which determine how slots are allocated.

Source
Definitions of levels by IATA, from Slot Coordination Switzerland:

Level 1: airports where the capacity of the airport infrastructure is generally adequate to meet the demands of airport users at all times.
Level 2: airports where there is potential for congestion during some periods of the day, week, or season which can be resolved by voluntary cooperation between airlines. A facilitator is appointed to facilitate the planned operations of airlines using or planning to use the airport.

Dublin and Salzburg are Level 2.
Level 3: airports where capacity providers have failed to develop sufficient infrastructure, or where governments have imposed conditions that make it impossible to meet demand. A coordinator is appointed to allocate slots to airlines and other aircraft operators using or planning to use the airport as a means of managing available capacity.

Heathrow, Gatwick, Barajas, Oslo, De Gaulle, Orly, Tokyo, Malpensa, Pearson are Level 3.

Many major airports are level 3, but only one US airport (JFK) has this classification.
Is there a reason US is seemingly deliberately different? What does that mean in term of practical scheduling by airlines? Is the difference apparent to a pilot?

Are we talking mandatory slot control for scheduled commercial operations only, or mandatory slot control for all operations, including nonscheduled and noncommercial? (JFK is the first case -- scheduled operators there must get landing slots, while nonscheduled or noncommerical operations there are accommodated on a capacity-permitting basis.)

Also, LGA and DCA require slots for unscheduled operations there...

@UnrecognizedFallingObject: I think this is for all operators that need slots, I have added definitions at the end of the question.


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How are aircraft wings protected against flutter - aerodynamic oscillations that can break bridges?
A wing and a bridge are both exposed to flutter, a transverse wind distorting them by resonance.
Aircraft flutter:

Aircraft flutter, source (video)
Bridge flutter:

US Tacoma-Narrows bridge collapse in 1940, source (video)
Both bridges and aircraft have been destroyed this way. How are wind/rain/resonance-created flutter prevented or controlled in airplanes? How is flutter tested in flight?

Both videos above deserve to be watched, to understand how flutter can be dangerous.

Related, maybe a dupe?

https://www.youtube.com/watch?v=qpJBvQXQC2M

Aeroelasticity is the name of the field you want to look up for this (also the name of a dreaded subject for engineering students).

Possible duplicate of What is the purpose of flutter testing?

Ah! Just read the question again, and I think I finally understand what you're asking: what can be done to counteract flutter, which is a phenomenon that can destroy bridges and aircraft wings. Is that right?

Super-related: https://aviation.stackexchange.com/questions/32849/how-was-flutter-mitigated-in-jets-such-as-the-f-15-and-f-16

Possible duplicate of How was flutter mitigated in jets such as the F-15 and F-16?

Flutter happens when the eigenfrequencies of two oscillations move close together so their motions can reinforce themselves mutually. When that happens, then the amplitude will increase with each oscillation, up to a point where the amplitude is big enough to break things. That is how bridges are destroyed: Ever more energy is accumulated in the structure, a tiny bit with every oscillation, until the total overwhelms the strength of the weakest part.
If the two eigenfrequencies are not close enough together, both motions will still exist but will normally be damped so they die down quickly after being excited, e.g. by a gust. A typical example is the wing bending motion: When the aircraft flies into an updraft, the wingtips flex up, elastic energy is accumulated and set free once the extra lift from the updraft dies down. The wingtips move down and will very briefly oscillate around their long-term vertical position.
Now add a free-flying aileron (mechanical control system with stick free). This also can oscillate around its long-term deflection angle. As long as the eigenfrequencies of both motions are sufficiently apart, they will not interact. This should be ensured throughout the normal flight envelope. However, flying faster will increase the aileron eigenfrequency, and in this case we should focus on the first antimetric bending motion of the wing. At one point the aileron frequency will come close to the wing bending eigenfrequency, and only then this particular flutter mode will happen.
The glider in the second picture of your question is the SB-9, a longer-span version of the SB-8 (which itself is flutter-free). The added span moved the wing eigenfrequencies down, so they met with the aileron frequency at a lower speed. Now flutter could be observed when flying at the right speed, but it could be stopped simply by gripping the stick.
Therefore, the possible protections against flutter are:

Limit the flight envelope. Prohibit flight speeds at which flutter is possible.
Increase damping. This can be as simple as adding some friction. The rudder cables in gliders are run in PE tubes which add some friction, eliminating rudder flutter.
Put mass balance on all control surfaces. On the Handley-Page O/100 bomber of 1916 it was enough to crosslink the two halves of the elevator, which stopped the first known case of flutter in airplanes.
Increase eigenfrequencies by increasing stiffness. In the SB-13 flying wing glider high modulus carbon fiber was used in the spar to shift the wing's eigenfrequency sufficiently up to avoid a coupling of the wing bending mode with the short period mode of the airplane
Increase eigenfrequencies by mass reduction: When a wing is made lighter especially towards the tips, e.g. by clipping the wing tips, its eigenfrequency will move up, shifting flutter speeds up. Conversely, by adding wingspan to the sound SB-8 design, the eigenfrequency of the SB-9 wing went down.
Change eigenmodes: By running the aileron pushrods near the wing shell, wing bending can effect an aileron deflection which helps to dampen the wing's bending mode.
Cross-coupling of eigenmodes: By reducing the wing spar sweep of the SB-13 by 3° relative to that of the whole wing, the bending motion causes wing torsion which reduces incidence when the wingtips are bent up and vice versa. This is similar to the pushrod trick and is an application of aeroelastic tailoring.

In a similar way, the forward location of the engines on an airliner wing creates an inertial torsion moment when the wing flexes. This increases damping, so this example could had equally appeared in the first point.
To ensure a design is free of flutter, a range of tests is performed prior to first flight and during flight testing. From this answer:

Since maybe fifty years every new design must go through a static
vibration test to check which elastic eigenfrequencies exist.
Analytical methods are used to predict the (speed dependent)
aerodynamic frequencies and the structure must be modified to remove
any possibility of resonance. Next, the airframe is tested in flight
at ever increasing speeds and with exciters at the tips of all
surfaces (those can be like the vibration motor in your smartphone,
only bigger, or, in the simplest of cases, the pilot moves the control
surfaces). At increasing speeds, the exciters are run through a
frequency sweep (typically from 5 to 60 Hz) and the resulting
amplitude is measured by strain gages or accelerometers.

Flutter is an aero-elastic problem, a complicated sort of spring-mass-damper issue. Complicated because spring, mass, damping and the applied force are linearly distributed over the wing span.
Basically, the problem is as follows:

The wing root is fixed to the aircraft fuselage, the wing tip is not fixed and can twist.
The air streaming over the wing creates lift, but also creates a twisting moment. A longish body in a fluid stream wants to position itself perpendicular to the stream, that is why we need empennages.
So the wing would like to position itself perpendicular to free stream - the tip is twisted by the stream, and stopped by the torsion stiffness of the wing box.
The torsion stiffness and the damping need to be sufficiently high to stop the construction from overshooting, and then being pulled back and overshooting, etc. Which is the failure mechanism in the video of the Tacoma Narrows bridge.

So the torsion stiffness of the cross section of the wing needs to be considered. It is mainly composed of cross section area and -shape, upper and lower wing skin thickness, and spacing of the ribs. These are the factors that need to be tuned to provide adequate torsion stiffness, but the shape and area are mainly determined by the aerodynamicists, not the structural engineers.
Image source
The wing is primarily dimensioned to counteract upward bending. In aircraft pre-design, some methods have been developed to estimate wing structural mass from the geometry. The original method developed by Torenbeek (Appendix C) underestimated actual structural weight, due to absence of torsional stiffness considerations in the estimation method.
The correction factor for the required structural wing weight to counteract flutter is given as:
$$ k_{st} = 1 + C \cdot \frac{{(b \cdot cos\Lambda_{LE}})^3}{W_{des}} \cdot (\frac{V_D / 100}{{(t/c)}_r})^2 \cdot cos\Lambda_{1/2}$$
For the Fokker 50 this results in a correction factor of about 4% of basic wing weight, which would be the extra weight required for preventing flutter. Notice that this is a problem where wing sweep actually helps: the sweep wants to twist the wing tip back to neutral. It also helps if the engines are mounted on pods underneath the wing, in front of the aeroelastic axis. In that case no extra structural weight is required for torsional stiffness increase

This is flutter. The ways to counteract the flutter, as found here (section Flutter Fixes), are:

Move the center of gravity of the wing closer to the center of twist.
Raise the frequency of the flutter by making the wing stiffer and lighter (better energy dissipation).
Tune shape and other characteristics with the help of computer simulations or wind tunnel.
Set the maximal allowed airspeed below the speed at that the flutter occurs.
During test flight, check if there is no flutter in the flight envelope.

The discipline that deals with flutter and other air-structure interactions is called "aeroelasticity".
Aeroelasticity analyses the dynamic modes of the structure taking into account the coupled effects of the air (that causes pressure change) and the effects of the deformed structure geometry on the flow.
Flutter is a nightmare for flight and is not simple to analyze accurately. Therefore designers keep flight regime away from predicted flutter speeds or conditions to mitigate the risk of losing the aircraft or redesigning the structure.
"Flutter survey" is the general name of the flight tests where engineers intentionally excite the relevant modes using flight test instruments, shakers, actuators; or using flight control system itself. These tests are candidates for getting out of control. Therefore there are automatic test-stop criteria and also override features in case the test crew determine any particular problem.


text:
What is the purpose of these winglets on the Chinese version of the An-2?
The Shijiazhuang (now part of AVIC) Y-5B, a Chinese version of the Antonov An-2, has winglets of a particular type:

Photo by Linshuo at Airliners.net
Quite a futuristic design for this old biplane of 1958, still in production. Not all version of the Y-5 have such wingtips though:

B-50AG. Photo by Weimeng, AirTeamImages
What are the advantages of these winglets in this case, compared to more common ones? Why only one the upper wing? Are they used on other aircraft?

They sure are reminiscent of the wingtip feathers of a soaring hawk or eagle or vulture.

As you said, the Y-5 and Y-5B are Chinese variants of the Antonov AN-2. The Wikipedia page gives this info on the Y-5B:

Shijiazhuang Y-5B-100 – Y-5B aircraft fitted with triple tipsails on the upper wing tips, which reputedly gave 20% higher climb rate and improved L/D ratio by 15%.

Here is a research paper on tipsails which may help a little bit.
There doesn't seem to be a lot of empirical evidence of the performance gains that China claims with the Y-5B. I can't find examples of the triple tipsail design used on any other aircraft.
Just look at the aircraft though, all the struts, wires, hinges, etc hanging out in the wind, and these 3 little tip sails improve L/D by 15% and climb rate by 20%? That's a hard pill to swallow. If it were that simple, it would be a feature of nearly every aircraft.

I'm perplexed as to why tipsails are not used on a large scale given that "sails fitted to the wing tip can reduce its lift dependent drag by up to 35%", "longitudinal  static stability  of  the  wing  was significantly improved" and "the wing tip sails showed their ability to break down and reduce the tip vorticity behind the wing".

I assume because winglets do the same thing for aircraft that don't need to be multi role, but not sure on multi role aircraft, maybe Peter will chime in.

@mins You guys should know by now how sceptical I am of all the claims made in support of winglets. Claiming 15% better L/D with these tiny additions is ridiculous. Same goes for stability claims and especially the nonsense about breaking down tip vorticity. This is simply snake oil, like this.

@PeterKämpf Dang, Peter, you ruin all the cool new stuff with your silly reality :)

@TomMcW: Fixed gear, bracing, struts all over the place, and those guys worry about wingtip vortices. Sheesh!

Your link to the research paper on tipsails has rotten away. Could you replace it, and perhaps include some of its contents inside your answer to prevent this from reoccurring?

@AEheresupportsMonica I will try and find it again, but I've forgotten it's contents in the past 3 years so I can't put the contents in here from memory.

@RonBeyer thanks for caring; I am interested in the topic so if I run into anything related I'll put a link in the comments.

"Tip sails", we all should recognize this feature on soaring birds.  Also similar to Fowler flaps.
This is a lift enhancing device for slow flight. On the wing tip, it may also serve to reduce the high AOA wing tip vortex, breaking it into smaller vortices.
But notice the birds do not use these at faster speeds, as their drag producing lift is not needed and AOA is lower.
So the tip sail designers may take a cue from birds and airliners, and retract them at higher speeds.  The Etrich Taub would lend itself to that type of wing tip.  Imagine unfurling them just before landing.


text:
What are the correct names for the two faces of an airfoil?
When representing a wing airfoil, often the low pressure is on the top side and the lift is positive:

In this case upper and lower sides are enough to understand the role of the surfaces, But this is meaningless for a rudder or for a compressor blade.
Are there names to identify the faces in relation with the direction of the lift. (In French specific names, extrados and intrados, are used in relation with camber.)

In Italian you would have Estradosso and  Intradosso like in French, but I never encountered similar terms in English. Also, I don't know if French is different, but in Italian "Estra-" and "Intra-" are w.r.t. the camber curvature, not the lift vector (or they would have to switch during inverted flight, for example)

You can call the two opposite sides suction side (for face on the convex side of the camber curve) and pressure side (for face on the concave side of the camber curve).
This has been used in a number of cases- for example in NASA Report CR-1767 Section Data for Thin, Highly Cambered Airfoils in Incompressible Flow:

.. flow separation on the pressure side at negative incidence angles and on the suction side at positive incidence angles.

for airfoils and in National Energy Technology Laboratory Handbook:

The airfoils are curved, convex on one side and concave on the other, with the rotor rotating toward the concave side. The concave side is called the pressure side of the blade, and the convex side is called the suction side of the blade.

for compressor blades.

In a very formal environment (like an engineering lecture), the upper side of a wing may also be referred as extrados and the lower part as intrados. This terminology comes from architecture. Archs in architecture have an intrados (inner concave part) being extrados the oposite side. Latin laguages, like french or spanish, use this names quite often in airfoil terminology.


text:
Why does an airliner fuselage have a constant section over its length rather than a tear drop shape?
It is usually stated than a tear drop shape is a good shape for aerodynamic efficiency:

Adapted from Nasa
On the other hand, fuselage on an airliner has most of the time a long cylindrical section with round/tapered ends. I understand an aircraft has other constraints than just having the lowest possible drag. It comes to mind a cylindrical shape allows the same number of seats in most of the rows and also prevents to increase the section of the forward cabin.
Without further explanation, it seems curious the fuselage has not a shape between a rounded cylinder and a tear drop shape which is often seen for gliders:

Source
Without going into deep details, what are the most important reasons preventing such design?

Note that even raindrops aren't raindrop-shaped.

I'd think the primary reason for not using this shape is the necessity of carrying passengers and cargo.

There are different bullet designs. Some have a parabolic nose. Others have noses shaped from two intersecting circles and have sharp points. Many airplanes have parabolic noses too, as it is very efficient.

On the other hand, fuselage on an airliner is most of time bullet shaped.

No, it is not. A “bullet shape” has a flat end, which is where most of the drag is generated (at subsonic speeds). But that shape is never used on flying vehicles except on rockets where the end is occupied by the rocket engines.
Instead, airliners always have a tapered “boat” tail, sloping gently enough to avoid separation (sometimes with help of strakes). The resulting shape is as if you split a droplet in the widest point and insert a piece of cylinder. And the difference in drag coefficient between pure droplet and droplet with cylinder section inserted is very small.
Still, a continuously varying shape is slightly better than the cylindrical section. And the early aircraft did have that. Likely the last one of those was the Lockheed Constellation. The shape was great aerodynamically, but it was expensive to build, it made it more difficult to ensure all elements have proper strength to withstand the pressurisation, every time they derived a larger version they had to redesign all frames and in operation it was not exactly convenient for loading either.
In contrast the tubular section is much easier to design, easier to make and when they want to make a bigger version of the plane, they just insert a couple more frames and mount stronger engines to match the increased weight—between A318 to A321 or between all variants of B737-MAX, vast majority of parts is the same and there is just different number of frames and different engines. And it's simple to load—seats are mounted on straight rails and containers simply slide in to the cargo bay. And the difference in drag is small enough that the cheaper manufacturing and practicality will easily offset the increase in consumption.

That's an interesting angle.

@mins: And deserves to be accepted. Again, the most votes don't show which answer is spot on.

This site is amazing. I was just about to ask the question "Why aren't aircraft like the Lockheed Constellation any more, when as I understand it from aerodynamics...".

A few things

One of the main objectives for glider flight is making it as aerodynamically efficient as possible. For airliners, it is to make it as economically efficient as possible. This means that it has to carry as much as passengers (or cargo; sometimes, there is little difference) for the given fuselage volume.
Glider type designs in airliners will increase the possibility of tail strike significantly.
What is good for low speed flight is not exactly great for the high speed flight regime. The loads associated are different.
The aerodynamic design of glider is based on one thing- there is no engine. This means that the drag has to be kept an absolute minimum for any meaningful flight time. The airline designer, however, has the luxury of engines- he/she can pay some penalty in the form of drag to improve other performance characteristics.
Any design is a tradeoff- the structure at the rear of a glider eats into its carrying capacity. It is tolerated because gains from reducing drag outweigh the added weight. However, this is not the case in an airliner.
Aerodynamic efficiency is not everything- there are aircraft which are blatantly inefficient aerodynamically, but fly anyway because they serve the purpose.
The wing carries the fuel in an airplane. A teardrop shaped fuselage would require the wing to be well ahead of the cg (or you have to strengthen and increase size of the fuselage where the spar passes through). This would increase the size of the horizontal stabilizer (or require lengthier fuselage), increasing weight.
There are practical issues too- fuselage shaped like this would increase the boarding/deboarding time, reduce potential for further development (its difficult to plug fuselage sections in that case) among others.

One important point is that you're considering only recreational gliders. If you consider gliders designed for transport, you can see that their shape resembles airliners- a good example would be the troop carrying gliders of WWII.

Airspeed Horsa; Public Domain, Link

Additionally I believe fuselage shape is also influenced to some degree by area rule.

Downvoted because you buried the only real reason why airliners have constant cross section fuselages in so many superfluous words. Look at @Jan Hudec's answer for enlightenment.

Airliners do actually have an elongated teardrop shape to them in a side profile.  In aerodynamics this is generally referred to as 'boat tailing' an object.
The glider has much more of a tear drop shape - and by that I take it you mean the tadpole like shape of the fuselage with a long slender tail - empty because there is no need for additional systems which are voluminous.  The pilot, avionics, controls, landing gear, etc. all fit into the forward pod without a problem.  All the tailboom really needs to carry are the control linkages and structure.  Here it makes sense to have a long slender tail, just strong enough for structural purposes while minimizing skin friction drag.
Now most of the fuselage of an airliner is taken up by the passenger carrying pressure vessel which has to remain very large in order to do that job effectively.  It's also long enough that it will reach from nose to tail of the aircraft such that very little additional length is required to provide effective tailplane authority for weight and balance purposes.  A long slender tailboom is. not necessary here.